[wasm] Fix bounds check for zero initial memory.

src/compiler/wasm-compiler.cc

Index: src/compiler/wasm-compiler.cc
diff --git a/src/compiler/wasm-compiler.cc b/src/compiler/wasm-compiler.cc
index c52b45269229296c1b93a7fbb31e3f945aa64c13..89d4e1da0717a95f8b635d401253641f7da0e066 100644
--- a/src/compiler/wasm-compiler.cc
+++ b/src/compiler/wasm-compiler.cc
@@ -2855,6 +2855,14 @@ void WasmGraphBuilder::BoundsCheckMem(MachineType memtype, Node* index,
   // Check against the effective size.
   size_t effective_size;
   if (size == 0) {
+    // TODO(gdeepti): Remove filler check used here to stash the size of
+    // memtype for when code is relocated.

[bradn, 2016/10/13 22:43:41]

Maybe a single reloc type will work after all?

If we make the first check always:
offset + memtype - 1 < size

And the second:
index < size - offset - memtype + 1

We can then drop each check based on if the minimum allowed size means the
condition is always true?

[gdeepti, 2016/10/14 01:28:44]

Done.

+    Node* cond = graph()->NewNode(jsgraph()->machine()->Uint32LessThan(),
+                                  jsgraph()->Int32Constant(0),
+                                  jsgraph()->RelocatableInt32Constant(
+                                      static_cast<uint32_t>(memsize),
+                                      RelocInfo::WASM_MEMTYPE_SIZE_REFERENCE));
+    trap_->AddTrapIfFalse(wasm::kTrapMemOutOfBounds, cond, position);
     effective_size = 0;
   } else if (offset >= size ||
              (static_cast<uint64_t>(offset) + memsize) > size) {